In recent years, there has been an increased focus on reducing emissions of greenhouse gases generated by burning fossil fuels. One solution for reducing greenhouse gas emissions is to exploit renewable sources of energy. In particular, energy derived from the wind has proven to be an environmentally safe and reliable source of energy.
Energy in wind can be captured by a wind turbine, which is a rotating machine that converts the kinetic energy of the wind into mechanical energy, and the mechanical energy subsequently into electrical power. Common horizontal-axis wind turbines include a tower, a nacelle located at the apex of the tower, and a rotor that is supported in the nacelle by means of a shaft. The shaft couples the rotor either directly or indirectly with a rotor assembly of a generator housed inside the nacelle. The generator produces electrical power which is conditioned by a power converter before being provided to a power grid. A plurality of wind turbines may be arranged together to form a wind park or wind power plant.
State of the art wind turbine electrical systems comprise a plurality of power converters, typically connected in parallel to the generator. Each power converter comprises within itself a multitude of semiconductor switching circuits, which are generally used for power rectification and inversion, coupled about a dc-link. Unbalanced electric and magnetic components are known to be detrimental to the performance of switched power converter systems. The effects are particularly acute when converters are operated in parallel.